This invention relates to a chroma generation system which produces a color video subcarrier signal for decoding by a home color television receiver. More specifically, it is for use in conjunction with home video games.
Color video signals include a color burst reference signal. When the actual transmitted color subcarrier signal is compared with its reference signal the corresponding phase angles and amplitudes produce various colors on the video display. The decoding scheme is designed in accordance with the standards set up by the National Television Standards Committee (NTSC). Such a system ultimately, of course, produces red, green and blue driving signals for the electron gun of color television receivers. But it is theoretically designed keeping in mind the phase and maximum amplitudes of the six highly saturated colors which consist of red, green and blue and their complements cyan, magenta and yellow.
Prior systems for producing discrete colors for video game applications have sought to generate phase shifted signals by either delay lines or as shown in Alles U.S. Pat. No. 3,723,652 combining a number of phase shifted square wave signals to produce the different color signals. Neither of these systems produced highly saturated colors corresponding to all of the six saturated signals of the NTSC standards. For example, with phase delay techniques, signals produced result in slightly different shades of pale green or pale blue. In other words, the phase angles of the various signals rarely if ever corresponded exactly to those of the most saturated colors in the NTSC color system.
Another problem inherent in producing color signals for use in video games is the necessity for complying with Federal Communications Commission (FCC) regulations regarding radiation of broadcast type signals. Since most video game circuits are integrated and necessarily of the digital type, high frequency components are present because of the digital square waves. Thus it is usually necessary to provide additional filtering to eliminate such high frequency components. For example, see the Alles patent.
In conclusion in all the above-described systems, signals are produced which are separated in phase by essentially uncontrolled angles which do not precisely correspond to the most desired highly saturated color. As such, the colors tend to be pale and not well-defined, and of incorrect intensity so as not to produce a pleasing asthetic effect.